The invention is particularly concerned with improvements in snap-in connectors for helical metal cable and conduit, such as metal-clad cable, armored cable and flexible metal conduit. A known connector of this type generally includes a cylindrical body having a leading end that snaps into a hole in the junction box, a trailing end that receives the helical cable/conduit, and inwardly extending, flexible fingers or tangs that are intended to seat in the helical grooves to lock the cable/conduit in the connector body and establish electrical contact.
Underwriters Laboratories Standard 514B requires connectors of the type described to pass several stringent performance tests. One test requires the connector to resist a cable pull-out force of 75 pounds for 5 minutes. Another test measures the electrical resistance of the cable/connector assembly when installed in a junction box. In this test, the voltage drop from the outside of the cable/conduit to the junction box should not exceed 50 millivolts.
Tests conducted on commercially available cable connectors as described above have not met one or more of the desired requirements. This is due in large part to the fact that the cable tangs or fingers do not seat properly in the helical grooves of the cable/conduit. The failure of the tangs to seat in the helical grooves results in poor pull-out strength and poor electrical contact so that the voltage drop across the cable/fitting interface exceeds 50 millivolts.